Prepare the pudding mixture by mixing the instant pudding and cold milk together in a large mixing bowl until well combined.
Stir in half of the Cool Whip until it’s fully blended with the pudding mixture.
In a 9 x 13 baking dish, place a layer of Nilla Wafer cookies on the bottom, then add a layer of sliced bananas.
Spoon half of the prepared pudding mixture over the banana slices, spreading it evenly.
Continue layering with more cookies, banana slices, and finish with another layer of pudding.
Spread the remaining Cool Whip over the top layer of pudding, cover, and refrigerate for at least two hours or overnight.